Publish date: 2.27.25
Dairy producers are making faster genetic progress than ever before, meaning genetics are constantly improving. Thus, genetic evaluations must evolve to ensure their accuracy and relevance. They must also adapt to include new data, the latest research, and breeding advancements introduced to the dairy industry.
That’s why it is important to understand the U.S. base change coming in April 2025. This blog will give you a high-level overview of what a base change is, why it occurs, and what its impact will be.
What is a Base Change?
Understanding the meaning of each trait on a genetic evaluation or bull proof, as well as the possible financial impacts they could have on your dairy, is crucial. In certain situations, a single-point movement—whether favorable or unfavorable—may not make much of a difference, but in others, the impact may be greater.
Every dairy animal with a genetic evaluation or bull proof based on Council of Dairy Cattle Breeding (CDCB) and Holstein USA data is compared to the breed population average, known as the base. As a reminder, traits are measured as predicted transmitting abilities (PTAs) relative to the base.
Every five years, this base is recalibrated in the U.S. to account for genetic progress made within the population for key traits like milk production, fertility, and health. In other words, think of a base change as a report card of how much genetic progress has been made when compared to the previous generation. Updating the base every five years provides a constant comparison between your herd and the set average and allows you to see genetic progress. However, as we move further away from the base year, it is important to remember that you are estimating animals based on an average that is behind, genetically, what the current herd is.
The current PTA base reflects dairy cows born in 2015, since the previous base revision was made in 2020. April 2025 is the next base change and represents dairy cows born in 2020. It’s important to keep these base change adjustments in mind, as they ensure that genetic evaluations remain relevant by comparing today’s animals against a more recent benchmark rather than historical averages.
What Changes Will You See?
The question you might be asking yourself is, “What changes will I see as a result of the U.S. base change?” The answer is the updated genetic evaluation may show lower figures than the previous evaluation for certain traits. This time around, you might see a more noticeable impact because of the large amount of progress that has been made. Never before in history have we made this much genetic progress between base changes.
Although traits for an individual bull or cow might appear lower, this does not imply that they have lost their genetic worth in your herd. Instead, it simply reflects the fact that the overall population has improved, and the baseline has been reset to align with the current genetic base. The same high-quality sires you have relied on will continue to offer the same benefits to your herd.
It will also be important to note that CDCB will also be updating Net Merit $ (NM$) in April 2025. NM$ ranks dairy animals on their combined genetic merit for nearly 40 economically important traits. NM$ will drop around 450 points and will be three digits once again and start with six, seven, or eight. There were no new traits added this time, but there were several updates to traits already included. The new formulation includes the following changes:
- Increase weight on Milk and Fat
- Decrease in Protein
- More emphasis on lower cow weight, impacting Body Weight Composite
- Less total weight on Fertility traits like Daughter Pregnancy Rate
- Increased emphasis on Cow Conception Rate
For customers with a milk market more focused on protein, this update in Net Merit $ could have you selecting animals that don’t help you meet your goals. Using a tool like Cheese Merit or a Custom Index might be a better alternative for your genetic selection.
Remember, NM$ is a fixed index and based on the national herd, giving you no flexibility to customize for your specific operation. That’s why we suggest utilizing a Custom Index, which gives you the power to choose the traits that matter most to you and appropriately weigh them.
A base change reflects the improvement in genetic progress of the overall population and resets the baseline to align with it.
Interpreting the Results of the U.S. Base Change
Because of the base change, it will be critical that producers selecting based on criteria adjust their thresholds. Why? With the great changes in some traits, not updating could result in not enough of the best bulls for selection. When adjusting your criteria, we suggest that you align your thresholds with the base change.
For example, if you were selecting for +1000 lbs. Milk before the base change, you can now select a bull that is +250 lbs. Milk and still get the same genetic value. Because of the amount of change made, you may want to reassess the levels needed for certain traits following the U.S. base change, such as Somatic Cell Score, Daughter Pregnancy Rate, Cow Conception Rate, Stature, Dairy Form, Rear Udder Height, and Rear Udder Width.
This is another opportunity to consider utilizing a Custom Index or other industry-provided index. The design of an index helps minimize the effect you see after a base change. A bull’s rank will not change because an index is not based on specific criteria and therefore accounts for the base change automatically. It has been proven that genetic selection based on an index leads to faster genetic progress when compared to criteria thresholds.
It is important to interpret the base change correctly as you begin to use the updated genetic evaluations in your genetic plans. Keep in mind the following when looking at the results.
- The genetic value of the individual bulls and cows has not changed—only their rankings relative to a new population standard have been adjusted.
- For those using Holstein Type traits, the linear shape will still be the same, just not as extreme.
- The base change highlights that genetic progress continues to be made since this is the most progress between a base change ever.
- Your genetic selection decisions should remain focused on your milk market, facility, management system, and operational goals.
The key part of this discussion is that the genetics have not changed, and the animals themselves have not changed. What has changed is how we view an animal’s genetic superiority.
While the next genetic base looks pretty different than it did in 2015, it’s exciting to see the sheer amount of genetic progress the industry has made, and that is something to celebrate! ABS is proud to be a part of advancing the industry through genetic progress. Over the past 80 years, we have been grateful to assist our customers in making a significant amount of genetic progress, and we look forward to doing so in the future.
To learn more about the U.S. base change, contact your ABS Genetic Advisor and complete the form below.
(608) 846 3721